Method for correcting tool parameters of a machine tool for machining of workpieces

ABSTRACT

A method for correcting tool parameters of a machine tool for machining workpieces includes recording measurement values of measured characteristics as actual values of at least one workpiece machined with the machine tool. The measurement values are compared with the default set values of the workpiece. The measurement values of at least two measured characteristics are recorded from at least two parameters of at least one measured characteristic and/or from at least one measured characteristic and from at least one parameter. An average for a tool correction value is calculated from the measurement values and the corresponding set values, with which a correction of the machine tool is performed.

FIELD OF THE INVENTION

The invention refers to a method for correcting tool parameters of amachine tool for machining of workpieces.

BACKGROUND

In the industrial manufacture of goods, such as cars, for example, it iscommon practice to measure measured characteristics and parameters ofthe various components. These measurements can be carried out in specialmeasuring cells with contacting or non-contacting measuring devices, forexample by measuring robots, as known from DE 195 44 240 A1.

The purpose of such methods is to determine possible defects of themeasured object during product development, product launch or duringmanufacturing. The disadvantage of this method is that variousadditional errors can occur during the measuring process, which preventor make it more difficult to determine the defects of the object. Thequantities manufactured in a controlled manufacturing process can be ina range between one-piece production and mass production. The parts aremanufactured in a production facility where different manufacturingtechniques and technologies can be integrated. Depending on the specificmanufacturing technology, the installation procedures of the plant mayvary. For example, if the parts are produced by milling or turning, theproduction plant may include a CNC machine, including programming meansbut also electronic control equipment.

The workpieces to be manufactured are specified by the nominal data in adrawing and/or CAD model, which define the theoretical dimensions of theworkpiece in combination with suitable tolerances. The tolerances definethe accepted deviations between the given theoretical dimensions of thenominal data and the actual dimensions of a manufactured workpiece.

The manufacturing processes also include a quality inspection step,where measures are taken to ensure the desired quality of themanufactured parts, i.e. to ensure that the percentage of “good” partsdoes not come below a defined minimum. The quality inspection stepconsists of two sub-steps:

-   -   a measuring step to determine the quality of the manufactured        parts by measuring suitable measured characteristics and        parameters with a suitable measuring device;        and    -   a correction step to improve the production quality if the        results of the measurement step show unsatisfactory figures.

Nowadays, in manufacturing processes of the type described above, themeasuring device that records the quality of the manufactured workpiecescan be, for example, a coordinate measuring machine or an articulatedarm measuring device, for example, an arm of the measuring robot.

If the measurements show that the deviations between the dimensions ofthe measured parts and the theoretical values defined in the nominaldata exceed the accepted tolerances, suitable parameter values of theproduction plant are changed to compensate for these manufacturingdefects. For example, on a CNC machine this could be the case if amilling tool changes its properties due to wear.

This change of the parameter values is, as known from practice, carriedout manually by experienced operators. This has the disadvantage thatonly operators with a very good knowledge of the general installationprocedures of the plant, the current structure of the plant and thecause of the manufacturing defects can make changes in the parametervalues.

This requires highly qualified personnel and furthermore, in many casesa time-consuming and costly trial-and-error method is required, as thecause of manufacturing defects is often not precisely known.

In the state of the art (US 2016/0202681 A), due to this reason it isproposed to use a method to control a manufacturing process of an objectin a production module and to compensate for errors occurring in themanufacturing process, which method includes the generation of actualproperty data, in order to avoid the described disadvantages. Thisinvolves a sample object manufactured according to the manufacturingmodel. According to this state of the art, when defects are detected, anadjusted manufactured model is produced.

Furthermore, the state of the art (U.S. Pat. No. 6,368,879 B1) includesa process for the manufacture of semiconductor devices, for exampletransistors, as well as components with integrated circuits, which forexample contain transistors. According to this state of the art,manufactured Poly-Gate lines are tested for their line width and asample average is formed. The sample average is compared with a setvalue and the manufacturing process is adjusted to increase or decreasethe Poly-etching time. A detection of a defect of a tool is not recordedaccording to this state of the art.

In addition, the state of the art (U.S. Pat. No. 6,449,526 B1) includesa process for an automated manufacture or re-manufacture of tools bygrinding the workpieces. According to this state of the art a constantproduction quality should be maintained and the interference factorssuch as temperature changes, wear of the grinding wheel and inaccuraciesin the mechanical system should be compensated. According to this methodbelonging to state of the art, a measurement of the workpiece is carriedout with sensors to determine whether a further processing of theworkpiece is necessary or whether the grinding process can be completed.The measurements carried out during the process allow the detection of apossible defect before scrap is produced. In accordance with the methodaccording to this state of the art, the measurement values are firstexamined to determine whether and to what extent a feature of interestdeviates from a desired value. A follow-up check leads to stabilisationif a prescribed threshold value is exceeded. In addition, a follow-upcontrol may be limited to cases where the characteristic of interestdeviates from the desired value at least a prescribed number ofconsecutive times. This method makes it possible to ignore smalldeviations from the desired value due to measurement errors caused bythe tool or sensor malfunctions. The radial and axial positions thusobtained can be used for further positioning of the workpiece foradditional grinding. According to this state of the art, a newpositioning of the workpiece is thus carried out. No correction of thetool parameters is performed.

SUMMARY

The technical problem underlying embodiments of the invention is tospecify a method for correcting the tool parameters of a machine toolfor machining workpieces, which allows the manufacture of workpieceswhich are automatically produced within the specified tolerance limitsor other specified limits without the need for highly qualifiedpersonnel.

Embodiments of the invention relate to the field of quality assurancefor manufacturing processes. In particular, the embodiments refer to amethod for controlling a production plant based on the measurements ofthe manufactured workpieces of the manufacturing process, the workpiecebeing defined by nominal data provided, for example, by a technicaldrawing and/or a CAD model, in order to compensate for the systematicerrors in the manufacturing process.

According to one embodiment, a method enables the correction of toolparameters of a machine tool for machining workpieces. Measurementvalues are recorded as actual values of at least one workpiece machinedwith the machine tool, and the measurement values are compared withdefault set values of the workpiece.

In this embodiment, the measurement values of at least two measuredcharacteristics and/or the measurement values of at least two parametersof at least one measured characteristic and/or the measurement values ofat least one measured characteristic and of at least one parameter ofthe same or of one of the measured characteristics are recorded. Anaverage value for a tool correction value is calculated from thesemeasurement values and the corresponding set values. The tool correctionvalue is used to correct the machine tool.

An advantage of the foregoing embodiment that, on the one hand, themachine tool can be subjected to a tool correction fully automaticallywithout the need for highly qualified personnel. On the other hand, themethod has the advantage that the measurement values of at least twomeasured characteristics and/or the measurement values of at least twoparameters of a measured characteristic and/or the measurement values ofat least one measured characteristic and of at least one parameter ofthe same or of another measured characteristic are recorded, and thatthese measurement values are compared with the associated set values andan average value is calculated for the tool correction value. This meansthat a tool correction value is not determined for a single measuredcharacteristic or a single parameter, which in some circumstances wouldmean that the tool correction might overcorrect another measuredcharacteristic or another parameter.

The term “measured characteristic of a workpiece” is understood to be acharacteristic of the workpiece to be measured, for example a groove, aslot, a bore, a trunnion, or the like. The term “parameters” areunderstood to be process parameters such as temperature, for example.Parameters can also be understood as machine parameters, such as spindlespeed, contact pressure of a tool or the like.

According to an embodiment of the invention, it is provided that aweighted average for the tool correction value is calculated from themeasurement values of at least two measured characteristics and/or fromthe measurement values of at least two parameters of at least onemeasured characteristic of the same or of another measuredcharacteristic and/or from the measurement values of at least onemeasured characteristic and at least one parameter.

This embodiment has the advantage that the measured characteristicsand/or parameters can be weighted. This means that sensitive measuredcharacteristics or parameters are more strongly included in the toolcorrection than the measured characteristics or parameters which are notso crucial regarding their tolerances or deviations.

This means that by taking into account different measuredcharacteristics or parameters, a tool correction value can be calculatedautomatically, which enables a correction of the machine tool, so thatall characteristics and parameters are corrected within the tolerancelimits or specified limit values without overcorrecting individualmeasured characteristics and/or parameters.

According to another advantageous embodiment of the invention, it isprovided that the measured characteristic and/or the parameter with thesmallest tolerance is mostly subject to weighting.

This embodiment ensures that an optimal correction of the measuredcharacteristics and/or parameters is carried out, i.e. that the “mostsensitive” measured characteristics and/or parameters are optimallycorrected, i.e. ideally close to the nominal value, while less sensitivecharacteristics and/or parameters are corrected so that the correctionlies within the specified limits or tolerance ranges.

According to another advantageous embodiment of the invention, it isprovided that each measured characteristic is assigned to at least onemachining tool. Each measured characteristic is machined by a machiningtool. For example, a bore is produced by means of a drill, or a trunnionis milled from solid material using a milling cutter. A measuredcharacteristic, such as a bore, can also be produced by severalmachining tools. For example, a bore can be produced by using a drilland then a milling tool. These machining tools are assigned to themeasured characteristic. This makes it possible to draw a conclusionabout, for example, the wear of the machining tool(s) if the measuringtool deviates from the nominal values.

According to another advantageous embodiment of the invention, it isprovided that the tool correction value is calculated smoothly from thelast n measurements (with n>1).

For example, the tool correction value can be calculated from the lastfive, ten or twenty measurements (n=5, n=10, n=20). This embodiment ofthe method according to the invention has the advantage that a toolcorrection is not carried out based on a single deviation, but rather acontinuous drift is detected with the method according to the invention.This drift is corrected by the tool correction value in the tool.

According to another advantageous embodiment of the invention, the driftis only corrected if the measurement values show a deviation from agiven limit value. The correction can also be carried out if themeasured measurement values show a deviation in the size of thetolerance value.

Another advantageous embodiment of the invention provides for the toolcorrection value to be visualised. This enables an operator to view thetool correction value and to monitor it as desired.

Another advantage is that the machine tool correction is carried outfully automatically after determining a tool correction value or after aconfirmation or after a confirmation after the visualisation of the toolcorrection value.

For example, the method according to the invention can be carried outfully automatically. The tool correction values are calculated accordingto the specifications, for example averaging or weighted averaging, andthe machine tool is automatically corrected with the tool correctionvalues.

However, it is also possible that the tool correction value isdisplayed, for example, and only after a confirmation by an operator isthe tool correction value used to correct the machine tool.

Another advantageous embodiment of the invention is that a toolcorrection is carried out after a continuous drift of a measuredcharacteristic and/or parameter has been detected based on the last nmeasurements and the measurement values exceed a given limit or a giventolerance value. This method ensures that a tool machine correction isnot caused by one-off manufacturing or measuring errors, but rather by acontinuous drift, for example when a milling tool wears out over time sothat no bores or trunnions can be produced within the tolerance ranges.

It is particularly advantageous that the threshold value, whichdetermines when a tool correction takes place, can be set. For example,a customer can establish when a tool correction is to be carried out.

According to another advantageous embodiment of the invention, it isprovided that additional parameters of external factors are taken intoconsideration when calculating the tool correction value. Such externalfactors can be, for example, the outside temperature, which affects thedilatation of the machine tool and/or the workpiece.

It is conceivable, for example, that after a machine standstill, e.g. atthe weekend or for maintenance purposes, the machine tool has a lowtemperature, i.e. a temperature below the operating temperature. Thiscan affect the manufacture of the workpieces. For example, if themachine tool returns to its operating temperature during operation, itis not necessary to constantly correct the “operating temperature”parameter. Similarly, an outside temperature can have an influence onthe manufacture of the workpieces.

Another advantage is that a work-offset correction is carried out if athreshold value or a tolerance value of the measurement values of ameasured feature and/or a parameter is exceeded.

In principle, it is possible to carry out a machine tool correction bychanging a travel range or, for example, by compensating a changedtravel range of an outwearing spindle drive. However, it is alsopossible to carry out a work-offset correction.

In the work-offset correction, the work-offset of a measuredcharacteristic or a group of measured characteristics is shunted. A newpoint of the measured characteristic or a group of measuredcharacteristics is defined as work-offset. The work-offset is the originof the coordinate system for the measured characteristic or group ofmeasured characteristics.

The work-offset correction is based on the position data of a measuredcharacteristic, which is a grouping of characteristics. For example, themeasured characteristic “bore” contains the characteristics “diameter”and “length”. The position of different measured characteristics inrelation to each other or to a reference point can be corrected.

According to an advantageous characteristic of the invention, it isprovided that the measurement of the workpiece is carried out in themachine tool and/or on an external measuring device. It is possible tomeasure the workpiece after manufacturing if it is still in the machinetool. This is possible, for example, with an articulated arm robot orsimilar.

However, it is also possible to measure the workpiece on an externalmeasuring device, for example a coordinate measuring device with tactilesensors, optical sensors, roughness sensors or similar.

Another advantageous embodiment of the invention provides for a datarecord, particularly a CAD data record of the workpiece, to be stored inthe machine tool to determine tool correction value. The data record,particularly a CAD data record of the workpiece, serves to provide themachine tool with set values for the workpiece. The data record may alsocontain tolerance limits.

Based on the data record, the machine tool can manufacture theworkpiece.

It is advantageous that the machine tool notifies if the measurementvalues of the measured characteristics and/or parameters are within thethreshold or tolerance values. The machine tool does not only givefeedback when a tool correction is made. The machine tool also providesadvantageous feedback if the measurement values of the measuredcharacteristics and/or parameters cannot be corrected. This makes itpossible to check that the measurement values are being monitored.

Another advantageous embodiment of the invention is that a toolcorrection value is calculated considering measurement values and/orparameters and considering past measurements. The parameters may beparameters of the measured characteristics, such as the temperature ofthe workpiece at the measured characteristic, and/or process parameters,such as spindle grinding pressure, and/or parameters of externalfactors, such as outside temperature.

This characteristic has the advantage that the process parameters can beconsidered for specific corrections. For example, after a standstill ofthe machine (after a weekend or maintenance) a temperature correction ismore often necessary than during operation. This correction-specificconsideration of process parameters is advantageously adapted to pastmeasurements, i.e. it is recognised that after each weekend atemperature correction is required more frequently when the operation isstarted.

Another advantageous embodiment of the invention is that tool correctionvalues for a first workpiece are transferred to the other workpieces. Itis basically possible, for example, that tool correction values arerecorded if bores are provided in a first workpiece because, forexample, drills or milling cutters wear out. These tool correctionvalues can be transferred for the machining of other workpieces, inwhich also bores are produced, so that with the tool correction thebores in the other workpieces can be produced indirectly within thetolerance limits or threshold values.

It is advantageously provided that the measurement values are recordedby the machine tool and/or by inline measuring systems and/or bymeasuring devices, especially coordinate measuring devices, articulatedarm or manual measuring devices. The measurement values can be collectedby all the devices used in the structure, i.e. by the machine toolitself or by inline measuring systems, i.e. measuring systems located inthe machine tool, such as scale monitoring for linear drives in the X, Yor Z direction.

According to another advantageous embodiment, it is provided that avisualisation and/or evaluation of individual measured characteristicsand/or parameters and/or tool correction data and/or a tool behaviour iscarried out. This makes it possible for an operator, who does not needto be highly specialised, to monitor the various values and takeappropriate measures in the event of a gross deviation.

It is advantageously provided that the measured characteristics aregrouped according to tools and/or work-offsets.

The work-offset is the origin of the workpiece coordinate system. Thiswork-offset is determined because workpiece blanks are of differentsizes and can be tensioned in different locations.

Several work-offsets can be defined for each machining program. Thedeviation of the position of one or more measured characteristics mustcorrect the assigned offset point by axis. The correction of the offsetscan also be calculated by weighting the individual measuredcharacteristics.

Essentially, it can be assumed that the measurement values of themeasured characteristics change when the assigned tools wear out, forexample. In this case, it is useful to group the measuredcharacteristics by tools so that different measured characteristics thatare machined with one and the same tool are corrected.

It is also advantageous that the workpiece is represented in graphics.

On the one hand, this allows the operator to see which tools areavailable. For example, the wear of tools can also be representedgraphically if the tool correction is required for the measuredcharacteristic produced with a specific tool.

According to another advantageous embodiment of the invention, it isprovided that when a project is created, a machine tool is selected, allavailable tools of the machine tool are displayed, a source for thequality data of the workpiece is selected and the quality data are readinto the machine tool.

When creating a project that involves the correction of tool parameters,a tool machine can be selected and all available tools for this machinetool are displayed, so that an operator can select the tools, forexample. In addition, a source for the quality data of the workpiece isselected either automatically or by an operator, i.e. the basic data ofthe workpiece to be manufactured are selected, including threshold ortolerance values. These quality data are read into the machine tool tomanufacture the workpiece.

Another advantageous embodiment of the invention provides that allavailable and active machine tools and/or the status of each machinetool and/or the project running on at least one machine tool and/orrecent events and/or tool correction values are presented on a displayof the machine tool and/or a computer connected to the machine tool. Theadvantage of this method is that it is possible to determine on whichmachine tool, which workpiece is being produced and how long themanufacturing process will take so that further or other workpieces canbe manufactured at a later date on a currently active machine tool. Theinformation of each project running on the machine tools or the lastevents and/or tool correction values are also displayed to monitor themachine tool.

The measuring devices used to measure the workpieces include, forexample, coordinate measuring devices, articulated arm measuringdevices, laser scanners, structural light measuring devices, coatthickness measuring devices, weighing devices, hardness measuringdevices, temperature measuring devices or devices for measuringvoltages, electric current, electric resistance and/or electricstrength.

The machine tool can be, for example, an additive manufacturing machine,a CNC machine, a pressing machine, a rolling machine, a wire and/orsheet bending machine, a wire drawing machine, a grinding and/orpolishing machine or a welding machine. The tools can, for example,provide a 3D printing, drilling, turning, milling, cutting, grinding,polishing, pressing, rolling, bending and/or welding function.

According to another advantageous embodiment of the invention, it ispossible to determine the remaining time of a tool. If the measurementvalues of a measured characteristic produced with a certain tool aredetermined for a certain tool and it is determined that a toolcorrection is necessary, it can be determined from these data when atool change will be necessary. This means that the remaining lifespan isdetermined.

It is also possible to define a threshold based on these measurementvalues. If the threshold is exceeded, a signal is output that a toolchange will be necessary after a certain remaining lifespan or aftermachining a certain additional number of measured characteristics orworkpieces. This means that an imminent tool change is notified. Thetool correction values are used to determine the remaining lifespan of aworkpiece. If specified limit values of tool correction values areexceeded, an extrapolation is made to determine the remaining runningtime.

For example, if a tool correction is performed after every 6,000 partsand the tool is usually changed after 50,000 parts, these figures can beused as a basis for verifying the need for a tool change or correction.This means that less frequent measurements are required, for example todetermine the remaining lifespan of a tool. For example, it is notnecessary to measure after 1,000 parts, but it is sufficient for a toolcorrection to measure after 5,000 parts to determine whether a toolcorrection is necessary after 6,000 parts. The change of a tool can bedetermined in the same way.

According to another advantageous embodiment of the invention, the lastn measurements (with n>1) can be used to determine whether an offset ofthe tool is necessary. In this case no further separate measurement isnecessary. The basis of the last n measurements determines when anoffset of the tool is necessary.

According to another advantageous embodiment of the invention, it ispossible to optimise the working conditions for the tools based onprocess parameters. For example, the process parameters and the pastoffset data can be used to determine the conditions under which a toolcan be used for a longer period. Thus, tool changes can be delayed. Forexample, it can be determined that a tool has a longer operating timewith only small temperature fluctuations.

It is also possible, for example, to determine the measurement valuesfor a tool via the spindle current of a drive spindle, which can be usedto achieve better manufacturing results. For example, a manufacturingspeed can be minimised by 10% and the measurement value for determiningthe tool correction values are used to determine that the reduction inmanufacturing speed results in 10% fewer out-of-spec parts, so thatoverall better manufacturing results can be achieved. The manufacturingprocess can thus be optimised.

According to another advantageous embodiment of the invention, anextrapolation of tool correction values is carried out considering pastmeasurements. Based on the past measurements, it is possible to predictwhen a tool is subject to such a high degree of wear that it must bereplaced. Based on past measurements, it can be determined, for example,that the tool must be replaced after machining 3,000 workpieces at atime.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention are shown in thecorresponding drawings, in which different characteristics of amanufacturing plant according to the invention are only shown asexamples without limiting the invention to these design examples. In thedrawings it is presented:

FIG. 1 a schematic representation of a manufacturing process;

FIG. 2 an overview of the method according to the invention with acontrol chart;

FIG. 3 Measurement values of a trunnion;

FIG. 4 Measurement values of a slot;

FIG. 5 a correction of the measurement values averaged from the valuesin FIG. 3 and FIG. 4;

FIG. 6 An enlarged display of the correction of FIG. 5;

FIG. 7 A flow chart for creating a project;

FIG. 8 A flow chart for the visualisation and calculation of toolcorrection data;

FIG. 9 A flow chart for the extrapolation of tool correction values.

DETAILED DESCRIPTION

FIG. 1 shows a manufacturing plant 1 in which the workpieces 3 aremanufactured from the blanks 2, for example by machining with a drill ora milling tool or similar. A measuring device, in this case a coordinatemeasuring device 4, is used to measure the characteristics of theworkpieces 3. These measurement values result in a control chart 5, inwhich the measurement values are recorded, namely the measurement values13 and the measurement values 14 of different measured characteristicsof the workpiece 3. In the present case, the workpiece 3 has twomeasured characteristics, namely a bore 6 and a second bore 16. Themeasurement values of the control chart are transmitted to an analysisunit 7, for example to a computer. The computer analyses the controlchart 5. If the values are stable and do not violate a threshold ortolerance value, there is no intervention in the manufacturing process.If the measurement values are not stable, an intervention takes place byfurther transmitting a correction value, which is determined from themeasurement values, to a process control device 8 or directly to thetool machine 9 of the manufacturing plant 1. In the tool machine 9, thetool correction value is used to produce workpieces 3 with a bore 6 or abore 16, which is within the tolerance range or within default thresholdvalues.

According to FIG. 2 the measuring machine 9 is shown as well as thecoordinate measuring machine 4. The process information 10 is stored inthe control chart 5, as already explained. If the control chart isstable, as in the area 5 a of the control chart, no action is taken,i.e. process branch 11 continues. If there is a larger deviation of themeasurement values from the nominal values, as shown in 5 b by theunstable measurement values, the process branch 12, i.e. processintervention is necessary.

FIG. 3 shows a representation of the measurement values 13 of the outercontour of a trunnion. The diameter Ø is plotted against the time t. Thenominal value is 25. If a milling tool used to produce the trunnionwears out over time, a drift occurs, which in the example shown runsagainst a fixed threshold value of 25.15 (OG) at the time t1. At thetime t2 a correction is performed so that the measurement values areback to the nominal value. At the time t3 a further wear of the millinghead becomes noticeable and the measurement values show again a drift.At the time t4 there is again a maximum approximation to the thresholdvalue 25.15 (OG), so that at the time t5 a correction follows again.

As the milling head wears off, the diameter of the milling head becomessmaller so that the diameter of the trunnion becomes larger.

FIG. 4 shows the measurement values of an inner contour of a slot. Thediameter Ø is plotted against the time t. Again, the diameter is plottedagainst time. When the milling head is worn, the inner contour becomeslarger and larger so that the inner contour drifts against a thresholdvalue of 24.8 (UG) at the time t1. A correction is made at the time t2.A further wear of the milling head causes the diameter of the inner boreto decrease again until the time t3, when the measurement value (14) ofthe diameter of the inner contour exceeds the threshold value 24.85(UG). At the time t4 a correction is performed.

In FIG. 5 the diameter Ø is again plotted against time t.

The measurement values 13 in FIG. 3 are mirrored and dotted at thenominal value 25 (NW). The measurement values 14 of FIG. 4 relating tothe slot are shown with a solid line. From these measurement values 13,14 an average 15 is determined, which is shown as a dotted line in FIG.5. This average 15 forms the tool correction value.

As already mentioned, the nominal value NW is entered in FIGS. 3 to 5 at25. An upper limit OG is 25.15. A lower limit UG is 24.85. The uppertolerance value OT is 25.25 and the lower tolerance value UT is 24.75.

Instead of the pure averaging as in FIG. 5, a weighting of thecharacteristics can also be carried out, so that, for example, the toolcorrection value of the trunnion according to FIG. 3 has a greaterweighting than the tool correction value of the slot according to FIG.4. In this case the average 15 in FIG. 5 is shifted in the direction ofthe measurement values 13.

As shown in FIG. 6, averaging has an influence on the correction. FIG. 6shows how the measurement values 13 of FIG. 3 run against the upperlimit value OG=25.15, i.e. there is a continuous drift. The correctiondoes not take place up to the nominal value NW=25 as in FIG. 3 but basedon the averaging to a nominal value greater than 25, for example 25.05.

Similarly, the measurement values 14 of the slot are corrected based onthe averaging in such a way that they are slightly overcorrected, i.e.not to the nominal value NW=25, but to a value below 25, i.e. 24.95 forexample.

FIGS. 3 and 4 show the measurement values of various workpieces measuredover time t. This means that not a single measurement data record of acharacteristic is recorded, but rather the drift is recorded over acertain period of time and/or over a certain number of workpieces orcharacteristics, for example five or ten characteristics, and then acorrection is performed.

FIGS. 3, 4 and 5 define upper tolerance values OT, lower tolerancevalues UT, upper threshold values OG and lower threshold values UG. Thetolerance values OT and UT are specified by the manufacturingspecification. The threshold values OG and UG can be defined.

FIG. 7 shows a flow chart for the creation of a project. In a first step17, the corresponding tool corrections are defined for the various toolsof a machine tool 9 (not shown in FIG. 7). Furthermore, 3 measuredcharacteristics are defined for the various workpieces. These values ofthe tools, the tool corrections and the measured characteristics areassigned one to another in step 18. The assignment can be doneautomatically or manually. In processing stage 19, a link is madebetween the tools and the measured characteristics and between the toolcorrections and the measured characteristics.

According to this method, each measured characteristic 6, 16 is assignedto at least one machining operation. Furthermore, the measuredcharacteristics are grouped according to tools and/or work offsets.

When creating a project, a machine tool is selected and all availabletools of the machine tool are displayed. Furthermore, a source for thequality data of the workpiece is selected and the quality data are readinto the machine tool.

FIG. 8 shows a flow chart for the calculation and visualisation of toolcorrection data. According to FIG. 8, parameters such as processparameters or process data of the external factors are also consideredin step 18 when calculating the tool correction value.

If a threshold value (OG, UG) or a tolerance value (OT, UT) of themeasurement values of a measured characteristic and/or a parameter isexceeded, an offset correction or a tool correction is carried out.

Measurement values are archived from past measurements. These are storedand saved as historical measurement values. A tool correction value canbe calculated considering the measurement values and/or parameters andconsidering the past measurements (historical measurement values).

Furthermore, a visualisation and evaluation of individual measuredcharacteristics and/or parameters and/or tool correction data and/ortool behaviour is carried out. The tools can be represented in graphicsupon visualisation.

When creating a project, a machine tool is selected and all availabletools of the machine tool are displayed. In addition, a source for thequality data of the workpiece is selected and the quality data is readinto the machine tool.

FIG. 9 shows a flow chart for the extrapolation of the tool correctionvalues. According to this design example, an extrapolation of the toolcorrection values is carried out, considering the past measurements.Based on the past measurements, for example, a point can be made as towhen a tool is subject to such great wear that it must be replaced.Based on the past measurements, it can be determined, for example, thatthe tool must be replaced after machining 5,000 workpieces at a time.This value is included in the calculation and an analysis unit decideswhether a tool- or work-offset correction is to be carried out.

It is also possible to transfer tool correction values for a firstworkpiece to other workpieces.

REFERENCE FIGURES

-   1 Manufacturing plant-   2 Blanks-   3 Workpiece-   4 Coordinate measuring device-   5 Control chart-   5 a Stable measurement values-   5 b Unstable measurement values-   6 Measured characteristic-   7 Analysis unit-   8 Process control device-   9 Machine tool-   10 Process information-   11 Process branch-   12 Process branch-   13 Measurement value trunnion-   14 Measurement value inside slot-   15 Average-   16 Bore-   17 Process step-   18 Process step-   19 Processing stage-   OT Upper tolerance value-   UT Lower tolerance value-   OG Upper threshold value-   UG Lower threshold value-   NW Nominal value

1. A method for the correction of tool parameters of a machine tool formachining workpieces, comprising: recording measurement values ofmeasured characteristics as actual values of at least one workpiecemachined with the machine tool; comparing the measurement values withdefault set values of the workpiece, wherein the measurement values thatare recorded relate to at least one of: at least two measuredcharacteristics; at least two parameters of at least one measuredcharacteristic; and at least one measured characteristic and of at leastone parameter of the same or one of another measured characteristic;calculating an average for a tool correction value from the measurementvalues and associated set values; and correcting the machine tool usingthe tool correction value.
 2. The method according to claim 1, wherein aweighted average for the tool correction value is calculated from themeasurement values.
 3. The method according to claim 2, wherein themeasured characteristic and/or the parameter with the smallest toleranceis used most strongly in calculating the weighed average.
 4. The methodaccording to claim 1, further comprising: performing an assignment ofeach measured characteristic to at least one machining tool.
 5. Themethod according to claim 1, wherein the tool correction value iscalculated continuously from the last n measurements (with n>1).
 6. Themethod according to claim 1, further comprising: visualizing the toolcorrection value.
 7. The method according to claim 6, wherein correctingthe machine tool is performed automatically after determining the toolcorrection value or after confirmation after visualizing the toolcorrection value.
 8. The method according to claim 1, wherein correctingthe machine tool is performed after a continuous drift of themeasurement values of a measured characteristic and/or a parameter hasbeen detected based on the last n measurements and the measurementvalues exceed a default threshold value (OG, UG) or a default tolerancevalue (OT, UT).
 9. The method according to claim 8, wherein thethreshold value (OG, UG) can be determined.
 10. The method according toclaim 1, wherein the tool correction value is calculated by consideringadditional parameters of external factors.
 11. The method according toclaim 1, further comprising: performing an offset correction when athreshold value (OG, UG) or a tolerance value (OT, UT) of themeasurement values of a measured characteristic and/or a parameter isexceeded.
 12. The method according to claim 1, further comprising:measuring the workpiece in the machine tool and/or on an externalmeasuring device.
 13. The method according to claim 1, furthercomprising: storing a CAD data record of the workpiece in the toolmachine for determining the tool correction value.
 14. The methodaccording to claim 1, further comprising: making notification by themachine tool if the measurement values of the measured characteristicsand/or parameters are within threshold values (OG, UG) or tolerancevalues (OT, UT).
 15. The method according to claim 1, wherein the toolcorrection value is calculated considering the measurement values and/orparameters and considering past measurements.
 16. The method accordingto claim 1, further comprising: performing an extrapolation of the toolcorrection values by taking into account past measurements.
 17. Themethod according to claim 1, further comprising: transferring toolcorrection values for a first workpiece to other workpieces.
 18. Themethod according to claim 1, wherein the measurement values are recordedfrom at least one of: the machine tool; an in-line measuring system; anda coordinate measuring device, an articulated arm, a manual measuringdevice, or another external measuring device.
 19. The method accordingto claim 1, further comprising: performing a visualisation andevaluation of at least one of: individual measured characteristics;parameters; tool correction data; and tool behaviour.
 20. The methodaccording to claim 1, further comprising: grouping the measuredcharacteristics according to tool- and/or workpiece-offsets.
 21. Themethod according to claim 1, further comprising: representing themachine tool and other available machine tools in graphics.
 22. Themethod according to claim 1, further comprising: selecting the machinetool when a project is created; displaying all available machine tools;selecting a source for quality data of the workpiece; and reading thequality data in the machine tool.
 23. The method according to claim 1,further comprising: displaying on a display or computer associated withthe machine tool, at least one of: all available machine tools; a statusof each available machine tool; a project running on the machine tool;recent events; and correction values.